Embedded coding has generated tremendous interest in video, image and audio processing. This is because embedded coding allows the encoder to terminate the encoding process at any point to meet a pre-determined target bit rate. Furthermore, the decoder can truncate the bit-stream at any point and is still able to obtain a reasonable good quality of the decoded video, image or audio. In other words, an ideal embedded coding system is able to provide rate-distortion optimized truncated bit-streams, making it an ideal coding tool for building systems with Fine Granularity Scalability (FGS).
A popular method to implement an embedded coding system is by sequential bit-plane coding (BPC) due to its simplicity. In BPC, input data vectors from a data source are represented in bit-planes, and the bit-planes are then encoded sequentially, starting from the most significant bit-plane which represents the most significant bits (MSB) of the input data vectors, to the least significant bit-plane which represents the least significant bits (LSB) of the input data vectors. In addition to its structural simplicity, such encoding sequence from the MSB to the LSB of the input data vectors satisfies a principle of the embedded coding process as disclosed in [1], wherein bits affecting the quality of the video/image/audio data most should be encoded first.
Generally, implementing a bit-plane coding that gives an optimized value of the rate-distortion curve is extremely complex and requires high computational resources. This is because for general data sources, there exists statistical dependencies among bit-planes as well as among data samples. In order to capture such dependencies, an entropy coder has to employ a frequency table with a large number of entries, which does not only increase the complexity of the entropy coder but may also result in large modeling cost [2] that eventually degrades the coding performance. Therefore, most practical implementations of bit-plane coding usually adopt a compromised approach to reduce the computational complexities, which unfortunately, result in performance degradation.
Hence, it is desirable to have a bit-plane coding process which gives an optimized value of the rate-distortion curve, which is of a low computational complexity, and yet does not result in substantial degradation in performance.